Re: [PATCH] kexec: do KEXEC_FILE_LOAD and fallback to KEXEC_LOAD if not supported.

[Dave Young <dyoung@redhat.com>]

On 02/23/18 at 09:29am, Petr Tesarik wrote:
> Hi Baoquan,
> 
> On Fri, 23 Feb 2018 07:20:43 +0800
> Baoquan He <bhe@redhat.com> wrote:
> 
> > Hi Michal,
> > 
> > On 02/22/18 at 11:24pm, Michal Suchanek wrote:
> > > The new KEXEC_FILE_LOAD is preferred in the case the platform supports
> > > it because it allows kexec in locked down secure boot mode.
> > > 
> > > However, some platforms do not support it so fall back to the old
> > > syscall there.  
> > 
> > I didn't read code change, just from patch log, I tend to not agree. There
> > are two options KEXEC_FILE_LOAD and KEXEC_LOAD, some platforms do not
> > support, why does some platforms not choose KEXEC_LOAD, the working one?
> > Why bother to make change in code? I believe there's returned message
> > telling if KEXEC_FILE_LOAD works or not.
> 
> Well... let me give a bit of background. As you have probably noticed,
> this syscall was originally available only for x86_64, but more and
> more architectures are also adding it now.
> 
> Next, kexec is actually called by a script (which locates a suitable
> kernel and initrd, constructs the kernel command line, etc.). The
> script must either:
> 
>   A. know somehow if the currently running kernel implements
>      kexec_file_load(2), or
> 
>   B. try one method first, and if it fails, retry with the other.
> 
> I agree that kexec(1) should probably allow the user to force a
> specific method, but I don't see the benefit of implementing fallback
> in an external script and not in kexec-tools itself.
> 
> OTOH if you want to push the fallback logic out of kexec-tools, then I
> would like to get better diagnostic at least. Letting my script parse
> kexec output is, um, suboptimal.

In Fedora/RHEL we use this in scripts by checking the arch first,
for distribution it is enough?  There are also some other arch dependent
options in kexec-tools, there is no way to just use same for every
different platform without checking in scripts. 

If your scripts is not for a distribution, I agree that it is indeed a
problem.
> 
> Petr T
> 
> > Thanks
> > Baoquan
> > > 
> > > Also provide an option to call the old syscall in case the new syscall
> > > fails with other reason than ENOSYS.
> > > 
> > > Also document the options.
> > > 
> > > Signed-off-by: Michal Suchanek <msuchanek@suse.de>
> > > ---
> > >  kexec/kexec.8 |  9 +++++++++
> > >  kexec/kexec.c | 41 +++++++++++++++--------------------------
> > >  kexec/kexec.h |  2 ++
> > >  3 files changed, 26 insertions(+), 26 deletions(-)
> > > 
> > > diff --git a/kexec/kexec.8 b/kexec/kexec.8
> > > index e0131b4ea827..7e4df723251d 100644
> > > --- a/kexec/kexec.8
> > > +++ b/kexec/kexec.8
> > > @@ -144,6 +144,15 @@ Load the new kernel for use on panic.
> > >  Specify that the new kernel is of this
> > >  .I type.
> > >  .TP
> > > +.BI \-s\ (\-\-kexec-file-syscall)
> > > +Specify that the new KEXEC_FILE_LOAD syscall should be used exclusively.
> > > +Otherwise KEXEC_FILE_LOAD is tried and when not supported KEXEC_LOAD is used.
> > > +.I type.
> > > +.TP
> > > +.BI \-c\ (\-\-kexec-syscall)
> > > +Specify that the old KEXEC_LOAD syscall should be used exclusively.
> > > +.I type.
> > > +.TP
> > >  .B \-u\ (\-\-unload)
> > >  Unload the current
> > >  .B kexec
> > > diff --git a/kexec/kexec.c b/kexec/kexec.c
> > > index cfd837c1b6bb..25328c02b508 100644
> > > --- a/kexec/kexec.c
> > > +++ b/kexec/kexec.c
> > > @@ -1166,7 +1166,7 @@ static int do_kexec_file_load(int fileind, int argc, char **argv,
> > >  
> > >  	if (!is_kexec_file_load_implemented()) {
> > >  		fprintf(stderr, "syscall kexec_file_load not available.\n");
> > > -		return -1;
> > > +		return -ENOSYS;
> > >  	}
> > >  
> > >  	if (argc - fileind <= 0) {
> > > @@ -1243,6 +1243,7 @@ int main(int argc, char *argv[])
> > >  	int do_unload = 0;
> > >  	int do_reuse_initrd = 0;
> > >  	int do_kexec_file_syscall = 0;
> > > +	int do_kexec_syscall = 0;
> > >  	int do_status = 0;
> > >  	void *entry = 0;
> > >  	char *type = 0;
> > > @@ -1256,19 +1257,6 @@ int main(int argc, char *argv[])
> > >  	};
> > >  	static const char short_options[] = KEXEC_ALL_OPT_STR;
> > >  
> > > -	/*
> > > -	 * First check if --use-kexec-file-syscall is set. That changes lot of
> > > -	 * things
> > > -	 */
> > > -	while ((opt = getopt_long(argc, argv, short_options,
> > > -				  options, 0)) != -1) {
> > > -		switch(opt) {
> > > -		case OPT_KEXEC_FILE_SYSCALL:
> > > -			do_kexec_file_syscall = 1;
> > > -			break;
> > > -		}
> > > -	}
> > > -
> > >  	/* Reset getopt for the next pass. */
> > >  	opterr = 1;
> > >  	optind = 1;
> > > @@ -1310,8 +1298,7 @@ int main(int argc, char *argv[])
> > >  			do_shutdown = 0;
> > >  			do_sync = 0;
> > >  			do_unload = 1;
> > > -			if (do_kexec_file_syscall)
> > > -				kexec_file_flags |= KEXEC_FILE_UNLOAD;
> > > +			kexec_file_flags |= KEXEC_FILE_UNLOAD;
> > >  			break;
> > >  		case OPT_EXEC:
> > >  			do_load = 0;
> > > @@ -1354,11 +1341,8 @@ int main(int argc, char *argv[])
> > >  			do_exec = 0;
> > >  			do_shutdown = 0;
> > >  			do_sync = 0;
> > > -			if (do_kexec_file_syscall)
> > > -				kexec_file_flags |= KEXEC_FILE_ON_CRASH;
> > > -			else
> > > -				kexec_flags = KEXEC_ON_CRASH;
> > > -			break;
> > > +			kexec_file_flags |= KEXEC_FILE_ON_CRASH;
> > > +			kexec_flags = KEXEC_ON_CRASH;
> > >  		case OPT_MEM_MIN:
> > >  			mem_min = strtoul(optarg, &endptr, 0);
> > >  			if (*endptr) {
> > > @@ -1383,7 +1367,12 @@ int main(int argc, char *argv[])
> > >  			do_reuse_initrd = 1;
> > >  			break;
> > >  		case OPT_KEXEC_FILE_SYSCALL:
> > > -			/* We already parsed it. Nothing to do. */
> > > +			do_kexec_file_syscall = 1;
> > > +			do_kexec_syscall = 0;
> > > +			break;
> > > +		case OPT_KEXEC_SYSCALL:
> > > +			do_kexec_file_syscall = 0;
> > > +			do_kexec_syscall = 1;
> > >  			break;
> > >  		case OPT_STATUS:
> > >  			do_status = 1;
> > > @@ -1456,16 +1445,16 @@ int main(int argc, char *argv[])
> > >  		result = k_status(kexec_flags);
> > >  	}
> > >  	if (do_unload) {
> > > -		if (do_kexec_file_syscall)
> > > +		if (!do_kexec_syscall)
> > >  			result = kexec_file_unload(kexec_file_flags);
> > > -		else
> > > +		if ((result == -ENOSYS) || !do_kexec_file_syscall)
> > >  			result = k_unload(kexec_flags);
> > >  	}
> > >  	if (do_load && (result == 0)) {
> > > -		if (do_kexec_file_syscall)
> > > +		if (!do_kexec_syscall)
> > >  			result = do_kexec_file_load(fileind, argc, argv,
> > >  						 kexec_file_flags);
> > > -		else
> > > +		if ((result == -ENOSYS) || !do_kexec_file_syscall)
> > >  			result = my_load(type, fileind, argc, argv,
> > >  						kexec_flags, entry);
> > >  	}
> > > diff --git a/kexec/kexec.h b/kexec/kexec.h
> > > index 26225d2c002a..7abcec796cae 100644
> > > --- a/kexec/kexec.h
> > > +++ b/kexec/kexec.h
> > > @@ -219,6 +219,7 @@ extern int file_types;
> > >  #define OPT_TYPE		't'
> > >  #define OPT_PANIC		'p'
> > >  #define OPT_KEXEC_FILE_SYSCALL	's'
> > > +#define OPT_KEXEC_SYSCALL	'c'
> > >  #define OPT_STATUS		'S'
> > >  #define OPT_MEM_MIN             256
> > >  #define OPT_MEM_MAX             257
> > > @@ -246,6 +247,7 @@ extern int file_types;
> > >  	{ "mem-max",		1, 0, OPT_MEM_MAX }, \
> > >  	{ "reuseinitrd",	0, 0, OPT_REUSE_INITRD }, \
> > >  	{ "kexec-file-syscall",	0, 0, OPT_KEXEC_FILE_SYSCALL }, \
> > > +	{ "kexec-syscall",	0, 0, OPT_KEXEC_SYSCALL }, \
> > >  	{ "debug",		0, 0, OPT_DEBUG }, \
> > >  	{ "status",		0, 0, OPT_STATUS }, \
> > >  	{ "print-ckr-size",     0, 0, OPT_PRINT_CKR_SIZE }, \
> > > -- 
> > > 2.13.6
> > > 
> > > 
> > > _______________________________________________
> > > kexec mailing list
> > > kexec@lists.infradead.org
> > > http://lists.infradead.org/mailman/listinfo/kexec  
> > 
> > _______________________________________________
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> > http://lists.infradead.org/mailman/listinfo/kexec
> 
> 
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Thanks
Dave

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